1. Field of the Invention
The present invention relates in general to a strain sensor and a method for providing a profile of the strain gradient of an object, and more specifically resides in the utilization of a poled, piezoelectric layer as a strain sensing medium of such a sensor.
2. Description of the Prior Art
A number of types of strain sensors are known in the art and moreover, the use of piezoelectric material in strain sensors is not new as evidenced by U.S. Pat. to Ayers et al, U.S. Pat. No. 3,750,127. The Ayers et al patent discloses a coaxially constructed strain sensor that has an inner conductor, an outer conductor substantially circumscribing the inner conductor, and a piezoelectric strain sensing medium interposed between and in firm contact with both conductors. An electronic sensing circuit is connected to the piezoelectric sensing medium to sense electrical charges generated by the medium as a result of subjecting the sensor to mechanical deformation or strain.
Although the Ayers et al sensor apparently provides a satisfactory means for detecting and indicating levels of strain, such sensor does not provide a remanent image of the surface strain gradient of an object.